In order to make observation with an electron microscope easy by preventing electrification due to irradiation of an electron beam, generally, a conductive film has been heretofore formed on the surface of a microorganism sample or the like having no conductivity. This practice serves as a motivation for forming a conductive film on a tissue surface of a microorganism for industrial application. However, the practice does not necessarily suggest specifically on what parts of what microorganism species, and for what applications, its benefits can be obtained by forming the conductive film.
Meanwhile, regarding an application of a conductive structure having a helical shape as an electric-wave (a radio-wave) shield or an absorber, JP-A 2000-027072 (Patent Document 1) discloses an example in which a helical carbon deposit formed by a vapor deposition method is utilized as an electric-wave shield or an absorber. However, the shape of the carbon deposit formed by the vapor deposition method varies due to influences of the concentration of a raw-material gas in a reactor or on a substrate, the composition of the raw-material gas, the temperature distribution, and the like. It is extremely difficult to efficiently grow a deposit having an orderly helical shape.
To avoid such instability of the vapor deposition method, JP-A 2009-221149 (Patent Document 2) discloses a method in which a piece of a vessel secondary wall having a helical shape is taken out from a vascular plant, and a conductive film is formed on the surface thereof for use as an electric-wave shield or an absorber. However, in the process of taking out the piece of the vessel secondary wall having a helical shape from the vascular plant, since an unnecessary portion around the piece has to be removed by a large amount, the raw material efficiency is low. In addition, to remove the unnecessary portion, a large amount of chemicals has to be introduced, and long processing time is required. For this reason, a more efficient production method has been demanded.